It should go without saying that, once a well is drilled, it is desirable to get a high percentage of the oil and gas (hydrocarbons) out of the well. With this in mind, there can be considered to be several stages in the life of a well. In the best case, there is a first stage where the hydrocarbon-bearing geologic formation into which the well is drilled exhibits such a high fluid pressure (formation pressure) that the oil flows straight up the wellbore propelled by formation pressure and can be produced very economically. Eventually, however, the fluid pressure of the formation decreases to an extent to where it cannot overcome the hydrostatic pressure of the column of oil in the well and, thus, the oil must be pumped out. It should be understood that throughout this document, the term fluid is used to include both liquids and gases such as the combination of water, liquid oil, and natural gases which are typically produced from oil wells.
Pumping is the focus of the second stage in the life of an oil well. The most widely used pumps are rod pumps in which the pump reciprocally pumps the oil out of the well. While rod pumps are the mainstay of the oil industry, they have many drawbacks. First of all, such pumps have limited efficiency since they are pumping only half the time, i.e., when the pump is moving in one direction, since the pump is being refilled when moving in the other direction. In addition, the flow rate from rod pumps is limited by the displacement of the pump and the speed of operation. Also, the natural gas which comes out of solution from the oil during production can create a gas-lock in the pump. Without liquids in the pump at all times, friction between mechanical parts in the pump may cause the pump to fail. At a minimum, to fix a gas lock in the pump, the pump must be stopped and re-spaced. Worse yet, if re-spacing does not solve the problem, a rod job may be required to replace the pump. This involves the employment of a costly workover rig to remove the rods and pump and affect the repair.
Another drawback of rod pumps is that they cannot tolerate contaminant solids such as sand in the produced fluid, because of the close tolerances in the mechanical parts in the pump. As a result, such contaminants may jam the pump, causing the need for a rod job. Another problem with rod pumps is the inherent pounding of the mechanical parts due to the reciprocating action of the pump. This pounding damages the mechanical parts and particularly may cause the rods in the well to fail. Lastly, rod pumps can typically only be used in straight and slightly-deviated holes, as well as holes that are vertical or close thereto. Even in reasonably straight holes, rod wear on the tubing frequently causes tubing leaks that are expensive to repair.
An alternative to the rod pump is a rotary rod pump which addresses some of the problems of the rod pump while leaving other problems unaddressed. The rotary rod pump does tolerate relatively more gas and sand than the rod pump, but still will not tolerate large quantities of either. In addition, the rotary rod pump is more efficient than the rod pump because it is not limited to producing oil during only half of the pump cycle. Similarly to rod pumps, the rotary rod pump cannot be used with highly-deviated or horizontal wells. Another problem shared by rotary rod pumps is the mechanical failure which can occur over time.
Despite these drawbacks, these mechanical pumps are typically used to produce oil from a well until the remaining pressure in the formation is so low as to not be economically viable to continue the pumping. When this occurs, the well is typically capped off and abandoned, this being the third and final stage in the life of the well.
There have been attempts, however, by others to design apparatus that would make it economically viable to continue to pump oil from such wells. This typically includes apparatus which rely on creating pressure differentials in the well in the vicinity of the geologic hydrocarbon-bearing zone and pumping the oil out with a fluid pumped down from the wellhead. Examples of such techniques are disclosed in U.S. Pat. Nos. 3,941,510 (Morgan), 3,991,825 (Morgan), 4,923,372 (Ferguson, et al.), 3,884,299 (McCarter, et al.), 3,894,583 (Morgan), and others. Many of these techniques share common problems. First of all, many of these techniques require a packer to seal off the annular region between the oil well casing and the production tubing. The problems of inserting and maintaining a packer in the oil well include the cost of the packer itself as well as additional rig time to install and remove the device in or from the well. Many of these techniques also include highly-complex apparatus at the bottom of the bore hole which have a variety of labyrinth-like passageways with close tolerances. While such apparatus may perform well in theory, the passageways of such apparatus are very likely to become clogged with contaminants such as the sand, paraffin, scale, and/or grit which are typically produced in such wells. In addition, some of these techniques require a plunger in the production tubing to force the oil up and out therefrom. Also, many of these techniques will not work in deviated holes. Another complicating factor is that many of these techniques have valves that are included in the complex down-hole arrangement. The control of these valves and the replacement thereof is obviously greatly complicated by their presence at the bottom of the hole. Another problem, common to many of these techniques is that the parts used in the apparatus are not rugged, standard oil field parts, but instead are highly-toleranced, sensitive, custom-built parts which may not stand up to the use and abuse which is typical oil field. Also, many of these techniques require a side tubing string outside of and parallel to the production tubing. It is also believed that some of these techniques are limited as to the oil well depth at which they may operate. Lastly, it is not believed that many or any of these techniques are operable to draw a vacuum on the geologic hydrocarbon-bearing zone so as to more completely deplete the zone of hydrocarbons.
It is against this background and the desire to solve the problems of the prior art that the present invention has been developed.